A railroad generally consists of a pair of longitudinally running steel rails mounted to transversely extending rail ties. The rail ties maintain the pair of rails a set distance apart, referred to as the “gauge”. The ties are embedded in crushed stone or slag to resist shifting of the rails as trains are run therealong.
The rails are mounted to the ties by securing brackets referred to as “tie plates”. A basic tie plate is a substantially flat rectangular member with a shallow channel extending across it to receive the lower flange of a rail. The bracket has holes extending through it adjacent the channel to receive spikes. The spikes are driven through the holes in the tie plates into an underlying tie, with the head of the spike extending over the edges of the lower flange of the rail, to secure the rail to the tie.
The conventional tie plates are reasonably effective for straight runs and fresh ties. A principal disadvantage with conventional tie plates is that they rely on spikes for securement. With continued passage of trains and weathering, the spikes eventually work out of their respective holes and the ties become “spike killed” as new spikes are not securely received by the worn-out holes.
Furthermore, in corners the lateral force of a train passing over the rails will cause lateral movement of the rails and the rails to become spaced apart further and the “gauge to widen”.
To provide more secure mounting of rails in corners, a different tie plate arrangement has been developed such as for example sold under the trademark PANDROL. These plates are secured to the tie by lag screws (sometimes referred to as “screw spikes”). The rails are held to the plates by spring clips which engage a receptacle in the tie plate and which extend over the lower flange of the rail.
Screw secured plates do provide significantly better securement than spike secured plates however suffer from the disadvantage that they are significantly more time consuming and labour intensive to install. A spike secured plate may be spiked in place by an automated spiking machine that runs along the track. A screw secured tie plate must have each lag screw individually installed by a rail crew and requires installation of the spring clips to secure the rail to the tie plate.
Installation time requirements are very important in the railway industry. Shorter installation times minimize disruption to rail schedules by requiring a smaller “window” of track downtime. Furthermore, a typical rail crew has about 25 persons. Prior art screw secured plates are slower to install than spike secured plates and the time required for a few crew members to install the screws delays the remainder of the crew therefore adding to installation costs.
In the event of derailment, screw secured tie plates are generally rendered unserviceable. This is because the wheels of any derailed cars strike the spring clips and that portion of the tie plate which retains the spring clips. This renders the spring clips unserviceable and the tie plates incapable of receiving new spring clips.
Conventional screw secured tie plates are useable only with No. 1 ties as the spacing between screw holes does not enable a secure installation on arrower No. 2 ties.
It is an object of the present invention to provide a rail tie plate which has the resistance to movement of a screw secured tie plate yet which may be installed, at least temporarily, at a rate similar to that of a spike secured tie plate.
It is a further object of the present invention to provide a screw securable tie plate which is securely attachable to both No. 1 and No. 2 ties.